Kuala Lumpur: Malaysia on Thursday formally declared missing flight MH370 to be an "accident" and its passengers and crew presumed dead, a step that opens the door for compensation payments but is likely to hit distraught relatives hard.

"It is therefore, with the heaviest heart and deepest sorrow that, on behalf of the government of Malaysia, we officially declare Malaysia Airlines flight MH370 an accident... and that all 239 of the passengers and crew on board MH370 are presumed to have lost their lives," civil aviation chief Azharuddin Abdul Rahman said in a televised announcement.